Very strange phenomenon, who can explain it?

This phenomenon is easy to see in places with coal piles, especially on sunny days after rain.

The rotten sawdust in the tree hole becomes dense and airtight after being soaked in rain, but that substance is very flammable. The sun's baking will make sawdust smoulder in the tree hole, but because the tree is alive, such a small amount of sawdust will not ignite the wet trunk.

These trees should have the same characteristics, that is, they are more likely to attract insects such as longicorn beetles, and it is the sawdust chewed by longicorn beetles that produces this strange tree smoking phenomenon.